Flying off course: Why migratory birds from Asia land in Europe

Apr 10, 2008
Flying off course
The new research findings also now explain why the only vagrants to have been seen by bird-spotters in Central Europe are long-distance migratory birds from Far East Asia. The genetically programmed journey for short-distance migratory birds from Asia would end somewhere in the west of northern Asia. Credit: Deutsches Zentrum fur Luft- und Raumfahrt (DLR) / modified from Susan Walter/UFZ

Migratory birds make mistakes in terms of direction, but not distance. These are the findings of a team of ornithologists and ecologists from the University of Marburg, the Ornithological Society in Bavaria and the Helmholtz Centre for Environmental Research (UFZ), writing in the Journal of Ornithology.

The scientists assessed several thousand reports of Asian birds from the leaf-warbler and thrush families that had strayed to Europe. They discovered that the distance between the breeding grounds in northern Siberia and the wintering sites in southern Asia was often similar to the distance between the breeding grounds and Europe. The more similar the distances and the more numerous a particular species, the higher the probability of this species of bird straying to Europe.

The birds' body size is not a factor. For a long time, people suspected that the vagrants had been blown off course by the weather. The new findings, however, support the hypothesis that the vagrant birds end up in the wrong wintering areas as a result of an error in their migratory programme. Since many questions still remain unanswered regarding the spread of the bird flu virus H5N1, there is increasing interest in research into bird migration. Experts believe, however, that it is unlikely that the virus is spread via migratory birds and suspect that it is spread through the international trade in poultry products. In any case, vagrants pose the lowest risk.

In the course of their research into vagrants in Europe, the scientists evaluated the body mass, wingspan, size of breeding area, distance between the breeding area and the wintering area and the distance between the breeding area and Central Europe for 38 species of migratory birds. Their source was the list of confirmed sightings in the Handbuch der Vogel Mitteleuropas (handbook of birds of Central Europe) from the start of ornithological records to the early 1990s.

Eight species from the leaf-warbler family and six from the thrush family caught the scientists' attention as vagrants. One species that was spotted particularly often was the Yellow-browed Warbler (Phylloscopus inornatus), which was reported by voluntary ornithologists in Central Europe around a thousand times between 1836 and 1991. This species breeds in the Siberian taiga south of the Arctic Circle and overwinters in the subtropics and tropics of South-East Asia. The other Asian leaf-warbler species were observed much less frequently, if at all, in Central Europe.

By contrast, five thrush species were reported nearly 100 times. If vagrants were brought by the weather, smaller birds should be blown off course more frequently than larger ones. However, using statistical analyses, the researchers were unable to find any correlation between the frequency of vagrants and their body size. In addition, the Yellow-browed Warbler occurs far too regularly for every sighting in Central Europe to be explained by 'unusual' weather conditions during migration.

The species most likely to land in Europe are the ones that are widespread in Asia and are as common there as their relatives the chiffchaff and European willow warbler are in Central Europe. "The more numerous a species is, the greater the probability that one of them will be 'wrongly programmed' and go astray," explains Dr Jutta Stadler of the Helmholtz Centre for Environmental Research (UFZ) in Halle/Saale. "They fly the same distance but in the opposite direction, which takes them to Europe. This is why we have relatively large numbers of vagrants from Asia here."

The scientists suspect the cause is an error in the genetic migratory programme. The flight direction and flight duration are passed on from one generation to the next. This means that migration is the result of a genetic programme, through which bird populations have adjusted to environmental conditions.

However, migratory birds can adapt to changes in environmental conditions over just a few generations. Their genes are responsible for the migratory restlessness that drives most of them thousands of kilometres to their winter quarters. Nevertheless, for a long time people were puzzled as to why individual birds of certain species repeatedly went astray.

"In these cases, errors have simply occurred in their genetic programming that, if you like, make the birds turn right instead of left. The vagrants can be compared to people who drive the wrong way down the motorway – they fly the wrong way down the intercontinental migration flyway," says Robert Pfeifer, General Secretary of the Ornithological Society in Bavaria.

"One can assume that for the majority of these birds, it is a one-way trip. Although there are indications that individual birds do attempt to overwinter in Southern Europe, none of them are likely to make the return journey to Asia. There have been no cases of ringed birds being found again that could provide information about what happens to them." The new research findings also now explain why the only vagrants to have been seen by bird-spotters in Central Europe are long-distance migratory birds from Far East Asia. The genetically programmed journey for short-distance migratory birds from Asia would end somewhere in the west of northern Asia.

Source: Helmholtz Association of German Research Centres

Explore further: Monarch butterflies rebound in Mexico, numbers still low

add to favorites email to friend print save as pdf

Related Stories

Sheriffs want popular police-tracking app disabled

51 minutes ago

Sheriffs are campaigning to pressure Google Inc. to turn off a feature on its Waze traffic software that warns drivers when police are nearby. They say one of the technology industry's most popular mobile ...

Obama recommends extended wilderness zone in Alaska

12 hours ago

US President Barack Obama said Sunday he would recommend a large swath of Alaska be designated as wilderness, the highest level of federal protection, in a move likely to anger oil proponents.

NASA craft set to beam home close-ups of Pluto

12 hours ago

Nine years after leaving Earth, the New Horizons spacecraft is at last drawing close to Pluto and on Sunday was expected to start shooting photographs of the dwarf planet.

Navy wants to increase use of sonar-emitting buoys

14 hours ago

The U.S. Navy is seeking permits to expand sonar and other training exercises off the Pacific Coast, a proposal raising concerns from animal advocates who say that more sonar-emitting buoys would harm whales ...

Recommended for you

Cellular memory of stressful situations

39 minutes ago

Stress is unhealthy. The cells use therefore a variety of mechanisms to deal with stress and avert its immediate threat. However, certain stressful situations leave marks that go beyond the immediate response; ...

Orangutans take the logging road

1 hour ago

A new discovery by a Simon Fraser University doctoral student in the School of Resource and Environmental Management, published in Oryx, demonstrates that orangutans may be even more adaptable than he fir ...

Picking up on the smell of evolution

2 hours ago

UA researchers have discovered some of the changes in genes, physiology and behavior that enable a species to drastically change its lifestyle in the course of evolution.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.